Main Entry: co·sine

Pronunciation: \ˈkō-ˌsīn\

Function: noun

Etymology: New Latin cosinus, from co- + Medieval Latin sinus sine

Date: 1635

1 : a trigonometric function that for an acute angle is the ratio between the leg adjacent to the angle when it is considered part of a right triangle and the hypotenuse
2 : a trigonometric function cos θ that for all real numbers θ is given by the sum of the alternating series and that is exactly equal to the cosine of an angle of measure θ in radians